wa_blame: better spec

Summary: - as title

Differential Revision: D107344055

fbshipit-source-id: 4a19a2b0706d54d4d45975ed494d57105179b47e

Author: ilya-klyuchnikov

src/wa_blame.erl

@@ -383,7 +383,7 @@ error_info(Reason, [{M, F, Args, _Meta} | _] = StackTrace) ->
             {error, no_error_info}
     end.
 
--spec match_expression(tree()) -> tuple().
+-spec match_expression(tree()) -> {match, erl_anno:anno(), dynamic(), dynamic()}.
 match_expression(Pattern) ->
     Anno = erl_anno:new(0),
     {match, Anno, Pattern, {var, Anno, '$VAR$'}}.